In automobiles having internal combustion engines or the like as engines, so-called an idling-stop or economy-running function is installed, in which, for the purpose of fuel reduction or exhaust emission reduction, an engine is automatically stopped in a state in which a vehicle is stopped and a braked pedal is operated by the driver, and in addition, the engine is automatically restarted by the user's restarting operation, for example, by reducing the operating amount of the brake pedal to zero.
In the vehicle having the idling-stop or economy-running function, when the engine is stopped and thereafter restarted, a voltage of a battery that supplies electric power to a starter may decrease due to driving of the starter. When the voltage of the battery decrease, a memory of an ECU (Electronic Control Unit) may be reset.
Then, as described in Japanese Patent Laying-Open No. 2010-255464 (PTL 1), it is proposed to stop an internal combustion engine if an estimated lowest voltage of a battery when the internal combustion engine is restarted after being stopped is higher than a prescribed value. As shown in the paragraph 35 and FIG. 2 in Japanese Patent Laying-Open No. 2010-255464, the lowest voltage is estimated by subtracting a voltage drop due to starting the motor from the voltage immediately before restarting the engine.